I'll be the pessimist here (since I'm in a funky bad mood tonight for no good reason).

If indeed the beer started tasting a little less good after a couple weeks, and its not so much a 'sour' or otherwise 'infected' flavor but just a 'its not as good'...I'd suspect oxidation. It causes the beer to go 'stale' sooner than it would in real life.

Porter is typically a beer that isn't great at first, but after a couple months in the bottle comes into its own. Teh more robust or imperial the porter, the longer it'll probably take to hit that peak flavor.

Many describe oxidation as a 'wet cardboard/newspaper' flavor.

Sometimes its just one bottle that got oxidized while filling. Sometimes the bottles don't age at the same rate.

And too, as beers mellow they can change several times. Especially with yeast in the bottle and priming sugar, the beer is 'alive and evolving' for some time.

Yep. Pessimistic and a rather huge leap to make given the little info we had. Nothing he said other than "A week and a half later" would suggest oxidation.

I know you have a lot more brewing experience than me, but that sounds like a pretty heavy-handed diagnosis to put in a newb's head...dontcha think?

Well. Ya I am a little overwhelmed with the feedback. This was only my first batch that I tried. The first batch like I said is okay but not really too great of flavor. My second batch has turned out much better. Anyways I understand what oxidation is in a sense of biology and technical terms. What exactly do you guys mean by the oxidizing in the bottles? How does that happen?